Portal stones appear as blue or orange gems. When dropped, they open a portal of the respective color.
Both, a blue and an orange portal stone, are needed to form a link. Entering a blue portal transports you to any orange portal and vice versa. You use portals just by walking and exit the other portal on the opposite side.
If multiple portals of the same color exist, a destination portal is chosen randomly. Place portals either at locations where they are easy to access from both seides (e.g. between two ladders) or put one color always to the right and the other to the left of a dungeon floor. Place portals in areas with a high ceiling. Take care from which side you enter.
Portals can also be used defensively. Enemies can be imprisoned between portals or you can dig yourself in behind or between portals.
Sometimes you end up on the wrong side of a portal. If possible, levitate over the portal to the desired side. You can also try to walk cautiously past without triggering the portal.
Pet management Edit
Nearby pets are sucked into the portal when you enter. That even applies to those pets you have ordered to stay. Humanoid pets are usually fine if they were close enough when you entered the portal.
To avoid any hassle, leave your pets a little distance away from the portal — preferably in a locked room.
A magic whistle can help. However, you can not summon pets over great distances. The summoning of the magic whistle seems to follow a straight line from the pet to the summoner — if there is a portal in this line, the pet will pass through, again beeing on the wrong side.
Portal stones are a reference to the Portal video game series. As in the game Portal, you need at least one of each for them to work.